This invention relates to an electret, and, more particularly, to an electret utilizing triboelectrically generated electrical charge.
An electret is the electric analog of a magnet wherein an electric dipole moment, or perhaps a multi pole moment, is more or less permanent and might be embedded within the material of the electret or might exist as surface charge. Historically, a wax such as Carnauba was,, is first melted and then allowed to cool under the influence of an electric field. Upon cooling molecular dipoles within the wax are frozen into an orientation determined by the field applied during cooling. The resulting bulk material is found to include a persistent internal electrical polarization and to exhibit the effect of long lasting charges of opposite polarity on it's surfaces. The historical name electret implies a dualism with a permanently charged magnet.
Electrets might also be created by ferroelectric effects wherein a ferroelectric material exhibits oppositely polarized charge on it's two surfaces as a result of applied pressure. Electrets might also be created in certain photoelectric insulating or semiconducting materials which might polarized internally under the combined influence of illuminating and a strong electric field.
It is well known that friction between dissimilar materials can result in electrification of the materials. Historically this effect has been the basis for a number of early electrostatic machines and electric shows. More recently, friction generated static electricity has been utilized to supply electric charge to toner particles in photo copying processes. The name given this process is triboelectric. During recent decades triboelectric processes have been explored extensively in conjunction with dry powder development in the photo copy industry. Toners are in common use which produce black or one of a number of colors. Toners are commonly available which posses special features, including magnetic and non visual features, including ultra violet or infrared features for producing magnetic or other specialty documents. By utilization of selected materials toners, including black and color, can be fabricated wherein either positive or negative charge is induced triboelectrically.
When two materials are brought into a frictional contact opposite charges might develop on the materials. The resulting polarities can be determined with an electrometer. By repeating this processes with a number of materials and arranging the materials in descending order from positive to negative a series of triboelectric activity can be defined. On such series from G. S. Rose and S. G. Ward, Brit. J. Appl. Physics, 8, 121 (1957)! is as presented below:
______________________________________ Positive: Ethyl Cellulose Casein PMMA Ebonite Cellulose Acetate Glass All Metals Polystyrene Polyethylene Teflon Negative: Cellulose Nitrate ______________________________________
Particles of these and/or similar materials, charged triboelectrically, form the basis for the toners used in a wide range of current photo copy products. Prior art technologies allow the creation of toner particles which might be triboelectrically charged to either polarity and these charged toner particles are available in a wide variety of colors. Toner colors of red, green, blue, cyan, magenta and yellow in particular are in common use in addition to black.
Toner particles might exist in clouds of individual charged particles wherein the particles are mutually repelled by their common charge. In the case of triboelectric electret particles, which might include equal and opposite charges on various extremities, the mutual repulsion dies not exist and such particles cannot by utilized in clouds. A convenient means of fabrication of triboelectric electret particles might be by means of fiber technology. For example, bundles of fibers of materials possessing different triboelectric properties might be first assembled and then cut into appropriate lengths, for instance by a focused laser beam. Following assembly of the said fiber bundles, they might be cut in place as part of an assembly procedure of the devices onto which they are to be included. Mechanical contact and/or friction might then be employed to produce an electric charges distribution on individual triboelectric electret particles.
Alternatively, a triboelectric electret might be cut from a single fiber which has been extruded from a plurality if material types.
Triboelectric surface charge densities might range between 7E-9 to 15E-8 Coulomb per cm.sup.2 (Rose and Ward, op. cit.). In a representative case of a multiple fiber triboelectric electret formed from either a fiber bundle or extruded or drawn as a single multi material fiber an electric charge might cover a surface area of 42 microns by 85 microns, or some 3.5E-5 cm.sup.2. At a surface charge density of 1E-8 Coulombs the charge on this area might comprise some 3.5E-13 Coulombs or 2.2E6 electronic charges. As a result of the discrete nature of electronic charge the actual charge might vary, having a one sigma variation of some 1,500 electronic charges. It might not be expected, apriori, that charges on the different extremities of a triboelectric electret would balance. A charge balance might be achieved or approximated, however, by control of the exposed areas of each of the triboelectrically active materials utilized.
Friction and/or repeated mechanical contact between materials exhibiting differing triboelectric activity is needed to establish and maintain the electric charge. An initial charge might be provided by acoustic means, whereby one of more triboelectric particles are agitated acoustically. Once charge is established the charge might be maintained by periodic agitation electronically. An external RF field might be utilized or electric signals might be supplied to electrodes which might be integral with an assembly.
Electret particles, which include separated charges of both polarities might find application in micro machines including visual displays. Micro machines commonly require a means of powered rotary or reciprocating motion. One form of prior art micro motors have employed vanes which have been fabricated by methods similar to the fabrication of VLSI integrated circuits and wherein the vanes are driven by commutated electrostatic fields. These prior art micro machine rotors often utilize materials common to integrated circuits, namely silicon along with various oxides and polymers. They have not been widely employed, mostly as a consequence of fabrication cost. The development and availability of cost effective micro machine motors will facilitate the development of micro machines for a number of potentially important applications, including specifically electronic display devices.
Prior art in the fabrication of fibers allow the production of fibers utilizing a wide range of materials, including glass, ceramics and many polymers. Utilization of these prior art fiber technologies for the fabrication of triboelectric electrets offers the potential of cost effective fabrication of electret particles. Fiber bundles composed of various fiber materials might first be assembled. These bundles might then be cut into particles which comprise small lengths of the bundles. Triboelectric electret rotors having two, four, or even more poles might by this approach be fabricated. The availability of a triboelectric electret rotor and/or translational positional element which might be positioned or driven by electric fields opens a wide range of possibilities and benefits in the emerging technologies of micro motors.
Prior art fabrication of multi glass optical fibers often starts with an optical preform which defines the final cross section of the resulting fiber. Using similar techniques a fiber might be fabricated starting with a preform which comprises a plurality parallel rods of glass of differing color, or other characteristics, which might have been fused into a single piece. Upon drawings into a fiber the resulting fiber will comprise a composite of the various glasses in a format defined by the preform. Capillaries, or hollow glass fibers, can be fabricated starting with a preform which includes a center which can be etched or otherwise removed following drawing into a fiber.
Triboelectricity is primarily a surface effect. If, following the drawings of a fiber, a polymer having triboelectric activity is laminated onto one or more of the exposed surfaces then the resulting fiber might exhibit triboelectric activity. A short length of this resulting fiber would then comprise a triboelectric electret element and might be either a solid fiber or a hollow capillary. By this means a triboelectric electret dipole or a multi-pole might be provided. A color gate might comprise a length of the said triboelectric electret element enclosed in an appropriate housing which might include drive electrodes. An array of these said color gates might comprise a color display device which might function under ambient illumination, thus eliminating the need, power requirement, and waste heat load of a self luminous display or of a dedicated external light source.
The propagation characteristics of a light beam can be changed by a number of basic means, including: complete or particle blockage, specular reflection as by a mirror, Lambertian reflection as by a diffuse reflecting surface, alteration of it's spectral makeup, or color, in a reflection or a transmission, alteration of the polarization properties, ray bending at a surface, and by diffraction by a grating. These means might be utilized singly or in combination to modify the characteristics of a light beam or of an incident illumination. The control of any one or some combination of these optical characteristics by electronic means offers the potential of enabling a display element which might function in ambient illumination, obviating the need for either self luminance or a dedicated light source for the display. The availability of motive power through the application of a triboelectric electret element provides the potential of the control of light by an optical gate which might employ any of combinations of the above discussed means. This capability in turn offers the possibility of arrays of light gates which might comprise a display for electronic data which might be free of the need for self luminosity and/of a dedicated light source, and which might work exclusively under ambient illumination.
In many important display applications, specifically those which are portable, the source of electrical power and the disposal of waste heat become dominate features in the design and cost. The availability of display elements which might work in ambient illumination thus offers considerable benefit in both function and cost.
It is an object of this invention to provide a triboelectric electret comprised of dissimilar materials wherein the dissimilar materials acquire opposite electric charges by triboelectric means.
It is a further object of this invention to provide a triboelectric electret dipole wherein the dipole might be oriented according to an external electric field.
It is yet another object of this invention to provide a triboelectric electret which comprises two or more electrostatic poles and which might assume any of a number of orientations under the control of external electric fields.
It is an additional object of this invention to provide an triboelectric electret element which might serve as the motive element in a motor or a micro motor.
It is another object of this invention to provide a triboelectric electret motive element which might be positioned rotationally and/or in reciprocation by external electric fields and wherein the optical and/or visual appearance of the element within it's local environment might be modified according to the motive element position when optical and/or visual attributes are included.